How do I delete a key

[groob]

The following manifest:

class bootstrap::munki($domain = '/Library/Preferences/ManagedInstalls.plist') {
include macdefaults
mac-defaults {'InstallAppleSoftwareUpdates':
domain => $domain,
key => 'InstallAppleSoftwareUpdates',
value => 'true',
type => 'bool',
}
mac-defaults {'SoftwareUpdateServerURL':
action => 'delete',
domain => $domain,
key => 'SoftwareUpdateServerURL',
value => 'http://fs2.whitbyschool.net:8088/index.sucatalog',
type => 'string',
}
}

when I run, I get "Error: Invalid parameter action"